This invention relates to a semiconductor integrated circuit device and also to a method for making the device. More particularly, the invention relates to a technique which is effective when applied to an interconnection structure and an interconnecting process of LSI having multiplayer interconnections.
In recent years, integration of LSI has been in progress. This leads to increased aspect ratios (i.e., the depth of a connection hole formed on an inter-layer insulating film between a given Al interconnection and a low conductor layer, semiconductor region or a lower Al interconnection. In order to prevent the breakage of the Al interconnections in the inside of the connection holes, a so-called tungsten plug technique has been utilized wherein a W (tungsten) film is filled in the connection holes.
To fill the W film up in the connection hole, a W film is deposited, according to the CVD method, on the entire surface of an insulating film in which connection holes have been formed. Subsequently, the W film on the insulating film is etched back, thereby leaving the W film only in the connection holes. For the etching back of the W film, a F (fluorine) plasma is used. In order to prevent the underlying insulating film (silicon oxide film) from being etched out with the F plasma, a underlying layer, which is constituted of stacked films including a Ti film and a TiN film, has been formed beneath the W film.
The underlying film constituted of the Ti/TiN stacked films is very resistant to electromigration or stress migration, and has been employed for interconnection of LSI which is fabricated according to the design rule on the order of submicrons.
Interconnections having such a stacked structure as of Ti/TiN/Alxe2x80x94Cu/TiN formed in this order and tungsten plug techniques for this are set out, for example,. in LVSI Multi-level Conference Jun. 7-8, 1994, pp. 36-43.
The semiconductor integrated circuit device to which the invention is directed is of the type which comprises three-layered metallic interconnections including a first layer made of a tungsten film, and second and third layers made of an aluminium alloy film, respectively.
A titanium (Ti) film and a titanium nitride (TiN) film, both serving as a underlying layer, are provided beneath the first-layered tungsten film. The interconnection for the first layer is constituted of a three-layered structure made of Ti/TiN/W formed In this order.
Likewise, a titanium (Ti) underlying film, a titanium nitride (TiN) underlying film and a titanium (Ti) underlying film are provided beneath each of the second and third-layered aluminium alloy (Alxe2x80x94Sixe2x80x94Cu) layers. Ti/TiN cap films are provided on each of the second and third-layered aluminum alloy (Alxe2x80x94Sixe2x80x94Cu) layers. More particularly, a six-layered structure of Ti/TiN/Ti/Alxe2x80x94Sixe2x80x94Cu/Ti/TiN as viewed from the bottom is established. As a matter of course, a tungsten (W) film is filled in connection holes connecting the first and second layers and the second and third layers therewith. Each tungsten film exists in the connection hole between the titanium nitride (TiN) underlying film and the titanium (Ti) underlying film formed on the TiN film.
We found that the semiconductor integrated circuit having such an interconnection structure as set out above has the following problems.
(1) The process of filling the tungsten (W) film in the connection holes essentially requires removal of the W film from the insulating film through etching-back by use of a fluorine (F) plasma as set out hereinbefore. This permits part of the fluorine in the plasma to be left on the surface of the underlying film (Ti/TiN stacked film) formed on the insulating film and exposed by the etching-back step. The thus left fluorine reacts with titanium to provide a solid compound. Hence, the compound is left on the underlying film. When another underlying film (Ti film) is formed on the first-mentioned underlying film, or when an aluminium alloy film is deposited subsequently to the etching-back step, the bonding force at the interface between the underlying film on which the compound has remained and the film formed on this underlying film lowers by the influence of the fluorine (F) residue.
Especially, the uppermost interconnection layer partly serves as a bonding pad. When a wire is bonded to the bonding pad, the pad may separate owing to the impact of the bonding. More particularly, it has been found that the underlying film on which the compound has been left separates from another underlying film formed thereon at the bonding pad portion.
(2) The process of filling the W film in the connection holes includes the etching-back step wherein the W film is allowed to be left only in the connection holes. This requires over-etching in order to completely remove the W film from the surface of the insulating film. At the time, the W film in the connection holes is also etched out from the outer surface thereof. This leaves a step between the surface of the insulating film or the surface of the underlying film and the surface of the W film in each connection hole.
In this condition, when an Al interconnection is formed on the insulating film, the Al interconnection is stepped at a surface portion just above the connection hole owing to the above-mentioned step. If a second connection hole is formed in the interlayer insulating film just above the first-mentioned connection hole in order to connect the Al interconnection and the upper Al interconnection therewith and the second connection hole is filled up with the W film, an insulating martial made of AlF3 is formed in the second connection hole at the time of the formation of the W film. This presents the problem that the conduction failure takes place between the Al interconnection and the upper Al interconnection.
Owing to the step appearing at the surface of the Al interconnection, the upper layer film formed on the Al interconnection suffers a coverage failure, thus Al being partially exposed from the upper layer film. The thus exposed Al reacts with F left at the time of the formation of the W film, thereby forming an insulating AlF3 film. This is the reason why there arises the problem that the conduction failure or an increase in contact resistance between the Al interconnection and the upper Al interconnection takes place.
(3) As having set out hereinabove, the Al interconnection is constituted of multi-layered interconnection (Ti/TiN/Ti/Alxe2x80x94Sixe2x80x94Cu/Ti/TiN). Usually, an uppermost interconnection is used as a bonding pad. However, if the uppermost interconnection is constituted of this type of multi-layered interconnection and part of a passivation film covering the uppermost interconnection therewith is removed by etching to form a bonding pad, a compound formed by reaction between Al and Ti is deposited at the interface between the Al film and the upper film (Ti/TiN stacked film) formed on the Al film. This compound is so hard that the bonding force between the bonding pad and a wire lowers. It should be noted that the etching of the passivation film does not make it possible to fully remove the compound of Al and Ti.
(4) The Al interconnections are formed by depositing the Al composite film by sputtering and dry etching the deposited film. If the coverage of the Al film on deposition of the Al composite film lowers by the influence of the step formed in the underlying layer, the processing accuracy of the interconnection through dry etching unfavorably lowers. To avoid this, a so-called high temperature Al sputtering technique has been proposed. In the technique, a semiconductor substrate is maintained at high temperatures, and the Al film is deposited while re-flowing the Al film by application of heat from the substrate, thereby ensuring a good coverage of the Al.
In this connection, however, when an Al film, particularly an Alxe2x80x94Sixe2x80x94Cu film or an Alxe2x80x94Cu film, is deposited according to the high temperature sputtering method, a reaction product is also precipitated in the film. The reaction product is left after dry etching, thus creating another cause of lowering the processing accuracy of the Al interconnection.
It is therefore an object of the invention to provide a technique whereby a bonding pad constituted of multi-layered interconnection is prevented from separation.
It is another object of the invention to provide a technique whereby an bonding force between a bonding pad constituted of multi-layered interconnection and a wire is improved.
It is a further object of the invention to provide a technique which is able to realize a stack-on-plug structure wherein connection holes for an upper layer are located just above connection holes of an interlayer insulating film, respectively.
It is a still further object of the invention to provide a technique wherein when an Al film is deposited according to a high temperature sputtering method, any reaction product is prevented from formation as precipitated in the Al film.
These and other objects and novel features of the invention will become apparent from the following description and the accompanying drawings.
Typical embodiments of the invention are summarized below.
According to one embodiment of the invention, there is provided a method for making a semiconductor integrated circuit device which comprises the steps of:
(a) forming a first insulating film formed on a semiconductor substrate and having a plurality of through-holes;
(b) forming a first underlying film on the first insulating film and in the plurality of through-holes and forming a tungsten film on the underlying film in such a thickness that the through-holes are filled therewith;
(c) etching the tungsten film to remove the tungsten film from said first insulating film thereby exposing the surface of the first underlying film and selectively leaving the tungsten film in the through-holes;
(d) sputter etching the surface of the first underlying film;
(e) forming a first metallic film on the sputter-etched first underlying film; and
(f) electrically connecting a metallic wire to the first metallic film in regions other than regions where the through-holes are formed.
According to another embodiment of the invention, there is also provided a semiconductor integrated circuit device which comprises:
(a) a semiconductor substrate;
(b) a first interconnection film formed on the semiconductor substrate;
(c) an insulating film formed on the first interconnection film and having a plurality of through-holes;
(d) a second interconnection film connected with the first interconnection film through the through-holes and formed on the insulating film; and
(e) a bonding wire connected to the second interconnection film, wherein the first interconnection film is constituted of a first aluminium alloy film, a titanium film formed on the first aluminium film, and a first titanium nitride formed on the titanium film, and the second interconnection film is constituted of a second aluminium alloy film and a second titanium nitride film formed on the second aluminium alloy film.
According to a further embodiment of the invention, there is provided a method for making a semiconductor integrated circuit device, which method comprising forming an aluminium film on a main surface of a semiconductor substrate by sputtering, characterized in that a first aluminium film is formed on the semiconductor substrate which is kept at a relatively low temperature, and a second aluminium film is formed at a substrate temperature which is higher than the first-mentioned temperature
According to a still further embodiment of the invention, there is provided a method for making a semiconductor integrated circuit device, which comprises the steps of:
(a) forming a first insulating film formed on a semiconductor substrate and having a plurality of first through-holes;
(b) forming a tungsten film formed on the first insulating film and in the first through-holes in such a thickness that the first through-holes are filled with the tungsten film;
(c) etching the tungsten film to remove it from the first insulating film until the surface of the first insulating film is exposed while selectively leaving the tungsten film in the individual first through-holes;
(d) forming a first aluminium film on the exposed surface of the first insulating film and on the tungsten film in the first through-holes; and
(e) re-flowing the first aluminium film at a given temperature.